from The Century Dictionary and Cyclopedia

Bound tightly by the hide, as an animal, or by the bark, as a tree: said of a horse, etc., when, from emaciation or other cause, the hide on its back or ribs cannot be loosened or raised in folds with the fingers; of a tree or a root, when the bark is so close or unyielding as to impede its growth.

Humankind's salvation is in their solar plexuses and not in their minds and in all that imaginary bullshit our minds accept as hidebound truth "hidebound" meaning some damn silly manmade book that supposedly contains OUR/THEIR god's HOLY WRIT.

The fibrous bundles of the true skin contain plain, muscular fibers, which are not controlled by the will, but contract under the influence of cold and under certain nervous influences, as in some skin diseases and in the chill of a fever, and lead to contraction, tightening, or corrugation of the skin, contributing to produce the "hidebound" of the horseman.